Pressure switch



N. J. SMTH PRESSURE SWITCH Oct. 26, 1948.,

Filed Jan. 18, 1945 Patented ct. 2?, 1948 PRESSURE SWITCH Norman J.Smith, Medeld, Mass., assigner to Fenwal Incorporated, Ashland, Mass., acorporation of Massachusetts Application January 18, 1945, Serial No.573,322

15 Claims.

My present invention relates to electric switches, especially those forcircuits to be opened or closed in response to pressure variation in afluid or other medium. It aims to improve such devices structurally andin performance, through novel features including compensation forambient or other temperature effects, avoidance of objectionabledistortion or deformation of operating parts, retention of pressurefluid against accidental escape and possible injury thereby, togetherwith other advantages which will be apparent from the followingdescription and accompanying drawings.

In the drawings illustrating by way of example certain embodiments ofthe invention, upon a somewhat enlarged scale:

Fig. 1 is a longitudinal section centrally through a pressure switchdevice, shown as having a relatively low pressure range, merely for thepurposes of illustration;

Fig. 2 is an outer or right end view of the device of Fig. 1; and I Fig.3 is a view corresponding to the left end portion of Fig. l, showingamodication, appropriate for but not limited to operation over higher ormore extensive pressure ranges.

Referring to the drawings in more detail, and first to Figs. 1 and 2,the pressure-switch device as a whole comprises a case or frameindicated generally at li, housing and supporting a switch unit 3U. Suchhousing herein includes a tubular shell 5, preferably cylindrical,having at one end a closing head 6 recessed as at 'I and having lappedengagement with the shell as at 8, the parts being united as by welding,brazing or the like, or they may be integrally formed. The case orhousing 4 further includes at the otheror inner end, integral with orsecured to it in lapped seating relation, a collar 9 centrally aperturedas at Ill in extension of the shell interior and having a lateralannular flange II. The collar 8 is adapted for connection to a chamberedbase I2 having a corresponding flange I3, the two flanges beingdetachably clamped together by screws or Kbolts I 4. This base hereincompletes the case or housing assembly.

The base I2 is of cup form presenting a chamber I5herein of largerdiameter than the bore of the shell 5 and somewhat flared toward thelatter. The base chamber I5 has an open inlet at I8 through anexternally threaded extension or neck I'l, by which the device as awhole is mounted at the point of use, in closed communication with thepressure medium to which the switch is to respond.

The base chamber I5 together with a conformant central recess i8 at theadjacent end face or thc collar t provide a space of substantial areatransversely of the device as a whole, for the operation of a pressurereceiving and transmitting element, herein a diaphragm 20 of a sheetmaterial of a strength and iiexibility as appropriate for the fluidpressures for which the given device is designed. The embodiment ofFigs. 1 and 2 is represented, merely by way of example, as having anoperating pressure range of from 0 to 15 p. s. i. (pounds per sq. in.),with an operating differential, as between the closed and the openstatus of the switch at the selected pressure within that range, of aslittle as 1 oz. It is constructed and arranged to afford a substantialsafety factor, herein that is, the device will sustain pressures abovethe intended range, up to 30 p. s. i. in the particular example. Asuitable diaphragm material in this instance is phosphor-bronze, e. g.Revere A or C, of about No. 20 to 22 gauge A. W. G. (approximately nl,in.)

The diaphragm 20 is replaceably held in operative position betweenopposed clamping faces 2 I, 22 on the collar 9 and base I2 respectivelyand desirably having mating annular rib and groove formations 23, 24 forgripping and sealing` engagement with the opposite faces of thecircumferential portion of the diaphragm. The clamping faces 2l, 22 areoffset lengthwise with respect to the meeting plane of the flanges II,I3, one face-carrying member, herein the collar 9, being recessed andthe other, here the base I2, being correspondingly shouldered, as at 25,26 respectively. The ybase I2 and the collar 9 together with the entirecase 4 are accurately aligned axially, while the break-joint relation at2E, 26 further seals the diaphragm peripherally.

A distinctive feature of the invention lies in the novel combination andmutual adaptation of direct pressure-actuated mechanical means,exemplied by the diaphragm and associated parts described, and anelectrical switch unit 30 of the Fenwal bowed-strut type. Such unitheretofore has generally been thermally actuated, through differentialexpansion or contraction as between it and a surrounding or adjacentcompanion element.

Switch units as here referred to comprise a pair of oppositely disposedconcave-convex flexible members. Strips or struts held together at theirrespective ends and carrying contact points centrally between them.These ilexible strips may bow in, for direct action wherein the switchcloses under longitudinal compression and opens on re- 'above or belowthe selected critical value.

lease thereof, or they may bow out for inverse actuation, opening theswitch' under longitudinal compression and closing it when relieved orunder tension lengthwise. For an example of a thermany-responsive Fenwalswitch unit of the direct or in-bowed type reference is made to Patent2,090,407 to Turenne; for the inverse or outbowed type of Patent2,185,433 to Fenn and Turenne; and for further disclosure of these twomain types and certain features broadly common to both of them, toTurenne Patent 2,257,990.

Similarly as in said Turenne Patent 2,257,990 the present invention isequally applicable to either and both the direct and the inverse switchtypes. For the purposes of illustration the switch unit 30 of Fig. 1 isshown as of the inverse or out-bowed type, operable to break contact ata predetermined thereof. It comprises a pair of spring strips or struts3|, 32 having their concave faces mutually opposed, with theircorresponding ends convergent and rigidly interconnected. Centrally at ythe inner faces of eachv strip 3|, 32 is a switch point 33, 34-ofsuitable electrical-contact material, such as silver, on clips 35, 36over mica, bre glass or other insulating material 31, 38.

In accordance with the present invention, such switch unit 30 isdisposed .axially in the tubular case 4 and is adapted for opening andclosing under the influence of longitudinal pressure, In the exampleof`Fig 1, the correlated means through which pressure acts on the switchunit includes the diaphragm 20, one surface of which is subject to thefluid pressure, or absence thereof, in the chamber I5.V

Accordingly one end of the switch unit is operatively connected, rigidlyin this instance, to the diaphragm. This is herein accomplished by aconnective head designated generally at 40, having a forked portion 4|in which the abutted ends of the switch strips 3|, 32 are secured as bywelding, brazing or the like. The head 40 has a tapped apertureoppositethe forked portion, receiving a screw-threaded member 42. Thelatter is formed with a flange 43, a rounded shoulder portion 44engaging the adjacent face of the diaphragm 20, and a reduced pin-likeextension 45 passing through a corresponding small aperture centrally ofthe diaphragm. The end of the pin extension 45 is turned down againstthe pressurereceiving face of the diaphragm, in attached sealingrelation to it.

Further in accordance with the invention, safety means is provided,herein associated with the diaphragm and the attaching head 40, againstaccidental escape of the pressure medium, whether steam, compressed air,hydraulic liquid -or other uid, in the event of rupture or other failureof the diaphragm under some abnormal condition, or to prevent undue orpermanent deformation of the parts under excessive pressure conditions.Such means as here shown comprises a valve element or safety plug 41integral with or fixed on the head 40, between the latter and the flange43 of the screw member 42.

This safety element 41, shown as a disc or plate having -a conicalseating formation 48, in effect selectible pressure lengthwise'constitutes a valve or closure plug, herein incorf the base-attachingcollar ,9 of the case 4 is formed with a correspondingly inclinedconical valvel seat 49, concentric with and communicating between theend recess i8 and the bore I0 of the collar. Normally the spacingbetween the valve 41-48 and its seat 49 is such as to ailord free actionof the diaphragm and the switch unit throughout the enttire operatingpressure range for which the particular device is designed.

At the other or outer end. toward the right in Fig. 1, the switch unit30 has rigid abuttive support in and with respect to the case 4, withcapacity for adjustment relative to it for pressure setting purposes.The adjustable supporting means for this purpose may be generallysimilar as in the patents mentioned. The outer ends of the switch strips3|, 32, which may be semi-cylindrical as in Fenn et al. Patent2,185,433, are confined in and secured to a tubular head 50 having alateral flange 5|.

This head 50 receives and is secured to the inner end of a pin or stud53. Along its outer end portion the stud 53 is externally threaded as at54 for reception in a sleeve 55 having corresponding internal threads56. This sleeve in turn has an external thread series 51 for cooperationwith a like-threaded formation 58 on the Wall of an axial openingextending through the casing head 6.

It will be understood that the cooperative thread formations 51, 58between the exterior of the sleeve 55 and the casing head 6, and theinterengaging thread formations 54, 56 between the stud 53 and theinterior of the sleeve 55 are respectively of a different pitch; thatfor the exterior threads of the sleeve desirably is somewhat lower.Rotation imparted to the sleeve 55 accordingly will effect adifferential action with respect to the stud 53, for shifting the latteraxially in one or the opposite directions through increments of thedesired fneness and accurately proportionate to the turning of thesleeve, in a generally similar manner as in the patents menfixed on it aknob 60 having an Vindex or pointer.-

6| for reading against a calibrated dial G2. The latter as shown ismounted concentrically with the sleeve 55, being positioned and held ona central boss 63 on a protective cupped flange 64 apertured for passageof the sleeve and secured flatwise against the head 6 of the case as atan annular shoulder 65 thereon. The switch unit as such may have aninitiaL normal or pre-installation status in which the contacts aresomewhat open and require an initial lengthwise tensioning of the stripsto close them, or in which the contacts are closed under more or lessinitial lengthwise compression of the strips, or the contacts mayinitially stand closed with the strips free of either compression ortension, depending on the construction, proportioning and arrangement ofthe parts. Hence, to indicate switchopening or closing) settings over azero to maximum range of pressure (above or below atmospheric) effectiveat the diaphragm, the scale, dial or other index means may be calibratedto include any appropriate plus or minus factor for the particularswitch unit.

From the respective insulated switch points 33, 34 insulated conductors10, 1| lead to the outside of the case 4, herein through a lateralopening 12 in the head 6. These conductors pass through sealing means13, such as impregnated asbestos packing, held in the bore of a tubularclosure nut 14 threaded into the casing opening 12 and externallyrecessed as at 'Il for attachmentvof ilexible armoring 1B through whichthe leads project.

Within the case 4 the conductors may be laid through notched edgeportions 52 of the ilange 5| on the switch head 50. Between the latterand the opening 12 they desirably are given one or more turns about anelongated tubular sleeve or shield 88. Such shield is heldin coaxialspaced relation to the threaded adjusting and switch-anchoring parts53-58, with its outer end secured in a recess for the pur-pose in thecasing head 6. t As a further important feature of the invention thedevice as a whole ,preferably is constructed and arranged to compensateautomatically.. to the desired extent, either fully or partially, forambient and other temperature effects upon it, or to make the switchresponsive either to pressure alone or to both pressure and temperature.For substantially complete independence of temperature effects,heat-subject parts including those of the housing case 4, the switchunit 30 and its supporting means are formed of materials which havesubstantially the same coeiiicient of linear expansion. In suchinstance, linear expansion and contraction under temperature variationsbeing opposite and equal or substantially so with respect to the case Iland the switch unit` 30, the switch is responsive to pressure only,through its entire operating range. In other instances, where a switchresponse is desired which is a function oi both pressure andtemperature, such conjoint response can be had by selecting materialsfor the case i, the switch unit 30 and the supporting means havinglinear expansion coeilcients in appropriate predetermined ratio otherthan l to l.

Referring now to Fig. 3, I have there shown a i'ui'ther embodiment oithe invention, especially suitable for relatively wide ranges cioperating pressure, again with adequate safety factor. For example, theswitch oi Fig. 3 may have a. normal operating range, exclusive of thesafety factor, irom 0 to Aloll p. s. i., or between other relativelywide-spread pressure limits, the setting means such as the scale or dialcorresponding to member 52 of Figs. 1 and 2 being graduated accordingly,as from 0 to 100. While the Fig. 3 embediment is particularly useful forextensive pressure ranges, including high pressures, it is not limitedto such use. Conversely the Fig. 1 iorm of the invention is adaptablefor other than low pressure purposes, the individual features of the twoillustrative embodiments being interchangeable, with such modificationof the diaphragm as to dimensions, strength and flexibility as may beappropriate for the pressures involved, with more or less spring-loadingif desired.

Parts not shown in Fig. 3 may be the same as in the preceding figures,otherwise than as to the scale or dial calibration, and like parts inFig. 3 have the salme reference numerals as in Fig. l, other parts beingnumbered with the addition of a zero.

In Fig. 3, the collar member indicated as a whole at 90 is formed withan externally threaded annular portion 9| while the base |20 has anoppositely extending sleeve |2| internally threaded to receive andsecurely hold the collar 9D, the shell 5 connected thereto and the case4 as a whole. The

diaphragm Z is firmly clamped at its circumference between gland rings|22. |23 held between noted, the embodiments of Fig. l and of Fig. 3

are not limited to low pressures and high pressures respectively, and ineither example the diaphragm structure, proportioning and arrangement inrelation tothe switch case may be varied as the particular operatingpressures and other use circumstances may require. As in the example ofFig. i, the outbowed strips 3|, 32 oi the switch unit 3B of Fig. 3 havetheir ends adjacent the diaphragm secured in a head 6U provided with ascrew member 42 including an end pin extending centrally through thediaphragm and having sealed engagement with it as at 45.

The safety means for blocking escape or" the pressure duid in case ofdiaphragm failure and for preventing 'undue or permanent deformation ofthe diaphragm and other parts is in this instance double acting. Withanextensive pressure range and particularly at the higher pressuresabnormally reduced or negative pressure conditions may arise, such as toplace undue stress on the diaphragm in the direction toward the left inFig. 3, as well as oppositely acting excess positive pressures.

Accordingly the valve of plug element dill, again oi' a disc-like formand similarly mounted on the head 40 as in Fig. l, is provided withoppositely inclined peripheral portions fiilil, del. These arerespectively adapted to have closed seating engagement withcorrespondingly inclined valve seats 490, 49|, one herein on the collar9B and the other on the adjacent clamping ring |23 of the diaphragm. Thelongitudinal spacing between these valve seats 490, l, and the thicknessof the valve disc 41B are relatively proportioned to afford the desiredtotal range of free action f or the diaphragm and associated switchparts. Thus it will be seen that in the event of rupture or failure ofthe diaphragm attendant on positive or relatively high pressures in thechamber ill, the valve "il will be received upon the seat de, toward theright in Fig. 3, while diaphragm failure in the presence of negative orrelatively reduced pressures will eifect a seating action as between thevalve and the seat 49|, toward the left in Fig. 3, again closing oif thecase d and relieving the switch unit from possible distortion orbreakage. Also, where excess oi positive or nega-tive pressure wouldcauseexcess motion of member 4B, with consequent deformation of theswitch unit or oi the diaphragm, this double stop acts to prevent suchdeformation. This double or two-directional stop feature, as well as theothers of Fig. 3, may be incorporated with those of the Fig. 1embodiment, and vice versa, as may be desired.

My invention is not limited to the particular embodiments as hereinillustrated or described, its scope being pointed out in the followingclaims:

I claim:

1. In an electric switch device. having a switch unit comprising a pairof metallic strips oppositely bowed in one direction along their workinglength and held together at their corresponding ends and a tubular caselongitudinally housing the switch unit, 'the combination therewith of anextension at one end of the case providing a pressure chamber having ailuid inlet, a pressure diaphragm transversely partitioning the chamberand the adjacent end of the switch strip pair, abuttive connecting meansbetween said end of the strip pair and the diaphragm, and rigidconnecting means between lthe other end of the strip pair and thecorresponding end of the case where--` by the switch unit is operativelysubject to pressure conditions at the diaphragm.

2. A pressure-actuated temperature compensated electric switch devicecomprising, in combination, a tubular metallic case having a closinghead and an opposite base for mounting the device in communication witha source of iiuid pressure, a pressure chamber in the base presenting aexible pressure-receiving diaphragm, an elongated switch unit comprisinga contact-carrying bowed metallic strut pair operatively responsive tolongitudinal forces thereon, said unit disposed lengthwise in the case,means rigidly connecting one end of the unit with the case head and theother end with the diaphragm, the case, the switch unit and saidconnecting means having a predetermined relation as to linear expansionproperties.

3. An electric switch comprising, in combination, an elongated bowedcontact unit, a supporting frame having rigid connection with one end ofthe contact unit, a flexible pressure-transmitting element connected tothe other end of the contact unit, and means for longitudinallysubjecting said element to variable uid pressure for correspondingresponse 4by the contact unit, the frame and the contact unit beingconstructed and arranged for equal and opposite longitudinal expansionand contraction whereby temperature eiects thereon are automaticallycompensated.

4. An electric switch comprisinain combination, an elongated bowedcontact unit, a supporting frame having rigid connection with one end ofthe contact unit, a flexible pressure-transmitting element connected tothe other end of the contact unit, and means for longitudinallysubjecting said element to variable Yiiuid pressure for correspondingresponse by the contact unit, the frame and the contact unit formed-ofmaterials having the coemcients of linear expansion in selected ratio tocompensate for temperature eiects to a corresponding predeterminedextent.

5. In a pressure switch, in combination with an elongated tubularsupport presenting a, uid pressure chamber having an inlet, a diaphragmsubject to pressures in the chamber, a bowed contact element extendinglengthwise in the support and operatively interposed as a strut b etweenthe. diaphragm and a stationary portion of the support, and pluralabutment means at the face of the diaphragm adjacent the contact elementand disposed respectively on the latter and on the support for opposingthe contact element and diaphragm in the event of abnormal pressureseiective thereon in either direction.

6. A pressure switch having, in combination, a tubular case, abowed-strip contact unit longitudinally disposed in the case with oneend rigidly held relative to it, said unit having contacts relativelymovable transversely of the case for making and breaking action and apressuretransmitting diaphragm transversely partitioning the case beyondand operatively secured to the other end of the contact unit in positionto subject it to pressure lengthwise of the unit and transverse to thedirection of contact making and breaking action thereof.

7. A pressure and temperature switch having, in combination, a tubularcase, a bowed contact unit longitudinally disposed in the case with oneend rigidly held relative to it, and a 'pressuretransmittingdiaphragm'transversely partitioning the case and operatively secured tothe other end of the contact unit, the case and contact unit formed ofmaterials having coemcients of linear expansion in selected ratio toafford predetermined relative effects of temperature thereon providingfor desired switch response as a function both of pressure andtemperature.

8. A pressure switch having, in combination a tubular case,l a bowedcontact unit longitudinally disposed in the case with one end rigidlyheld relative to it, and a pressure-transmitting diaphragm transverselypartitioning the case and operatively secured to the other end of thecontact unit, the case and contact unit formed of materials havingsubstantially the same linear expansion coemcients and wherebytemperature eects thereon are fully compensated and the switch maderesponsive to pressure only.

9. In a pressure switch, in combination, a case comprising a tubularshell, a closure head and a mounting base having a fluid inlet, apressure chamber in the case in communication with the inlet, a ilexiblediaphragm held in and normally closing the chamber, a bowed-stripcontact unit longitudinally interposed in the manner of a strut betweenthe diaphragm andthe case head, connector means between the contact unitand the diaphragm, a, valve-like stop and closure element carried by theconnector means at the side of the diaphragm away from the inlet, andseating means on the case cooperable with said element to opposeexcessive pressures and for sealv ing reception of said element toprevent escape of fluid past the diaphragm.

1U. In an electric switch, in combination, a'

case comprising a tubular shell, a closure head and a mounting basehaving a fluid inlet, a pressure chamber in the case in communicationwith the inlet, a exible diaphragm held in and normally closing thechamber, a bowed-strip contact unit longitudinally interposed in themanner of a strut between the diaphragm and the case head, and rigidmeans connecting the opposite ends of the bowed-strip unit with thediaphragm and with the case head respectively, the bowed-strip unit andthe shell having such relative linear expansion properties that thepressure setting of the switch is automatically compensated fortemperature variation to a predetermined extent.

l1. A pressure switch comprising, in combination, a. tubular case havinga closing headand a fluid-admitting base, a exible diaphragmpartitioning the case and subject to the uid pressure at one'face, abowed switch unit operatively disposed lengthwise between the diaphragmand the case head, rigid means connecting the diaphragm and the adjacent.end of the switch unit for longitudinal pressure variation upon theunit according to pressurev of the diaphragm,

' a stud connected to the other end of the unit and rotativelongitudinally adjustable means rigidly interconnecting the stud and thecase head,l

' of correspondingly enlarged surface area.

13. A pressure switch according to claim 11 wherein the eil'ective area.of the diaphragm is not greater than the approximate transverse area. ofthe case.

14. A pressure switch comprising, in combination, a tubular case havinga closing head and a fluid-admitting base, a, flexible diaphragmpartitioning the case and subject to the fluid pressure at one face, abowed switch unit operatively disposed lengthwise between the diaphragmand the case head, and rotative longitudinally adjustable means rigidlyconnecting the end of the unit distal from the diaphragm to the casehead and accessible externally of the latter for tensioning or relievingthe switch unit thereby to set it for action at a selected diaphragmpressure within a given range, said adjusting means including a scalegraduated in pressure units and calibrated to a minimum-maximum range ofdia'- phragm pressures, an index movable over the scale, and amanipulating member therefor.

15. An electric switch comprising an elongate hollow body having a headat one end, a pressure chamber with a fluid inlet at the other end ofthe body, a fluid-pressure diaphragm transversely partitioning thechamber, a bowed-strip contact REFERENCES CITED The following referencesare of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,370,193 Crocker Mar. 1, 19211,938,327 Green Dec. 5, 1933 2,086,264 Gorschalkl July 6, 1937 2,185,433Fenn et al. Jan. 2, 1940 2,275,556 Rasmussen Mar. 10, 1942

